EVD

Physical Forces

EVD 2

EVDPhysical Forces

Directly Influence Control

Offer Boundaries If Maintained – safe operation If Exceeded – loss of control

Ref. Unit IV LP 1 (Lesson 8)

EVD 3

EVDPhysical Forces

Forces Acting on an Emergency Vehicle Velocity Friction Inertia Momentum Reaction Centrifugal Force Centripetal Force

Ref. Unit IV LP 1 (Lesson 8)

EVD 4

EVDPhysical Forces

Inclement Weather Excessive Acceleration Inappropriate Braking Sudden Direction change

Ref. Unit IV LP 1 (Lesson 8)

EVD 5

EVDPhysical Forces

Velocity (Speed) “Rate of change of position in

relationship to time

V = 35 feet every second (35 ft/sec) V = 55 miles every hour (55 MPH)

Ref. Unit IV LP 1 (Lesson 8)

EVD 6

EVDPhysical Forces

Velocity Control Acceleration

+ Acceleration Deceleration

- Acceleration (Coasting)

Braking Deceleration using Friction

Ref. Unit IV LP 1 (Lesson 8)

EVD 7

EVDPhysical Forces

Friction “Resistance to motion between to

moving objects that are in contact with each other.” Generates HEAT

Steering Friction Tire/Road Friction Brake Friction

Ref. Unit IV LP 1 (Lesson 8)

EVD 8

EVDPhysical Forces

Friction Tire/Road

Greatest – Stationary Ok – Motion on Dry, Smooth Road Least – Locked/Spinning

Locked – Wheel NOT turning Spinning – Wheel FREE turning

Ref. Unit IV LP 1 (Lesson 8)

EVD 9

EVDPhysical Forces

Friction Brakes

Brakes on Drums / Pads on Discs Friction Generates Heat

Heat Causes Brake Fade Will Break-down Bonding Material Heat/Expand Brake Fluid

Ref. Unit IV LP 1 (Lesson 8)

EVD 10

EVDPhysical Forces

Brakes Shoes / Drums

90%-10% / Contact-Cooling Excessive Heat = Less Contact

Pad / Disc 85%-15% / Cooling-Contact Excessive Heat = More Contact

Ref. Unit IV LP 1 (Lesson 8)

EVD 11

EVDPhysical Forces

Brakes Locking Wheels Threshold Braking

Ref. Unit IV LP 1 (Lesson 8)

EVD 12

EVDPhysical Forces

Inertia “The force it takes a moving object to

stay in motion in the same direction.”

Ref. Unit IV LP 1 (Lesson 8)

EVD 13

EVDPhysical Forces

Newton’s First Law:

The Law of Inertia

Ref. Unit IV LP 1 (Lesson 8)

“An object continues in its state of rest, or uniform motion in a straight line,

unless it is acted upon by a net external force.”

EVD 14

EVDPhysical Forces

Newton’s First Law:

The Law of Inertia

Ref. Unit IV LP 1 (Lesson 8)

Objects resist change More Mass = More Inertia

EVD 15

EVDPhysical Forces

Momentum Mass x Velocity

Ref. Unit IV LP 1 (Lesson 8)

EVD 16

EVDPhysical Forces

Newton’s Second Law:

The Law of Momentum

Ref. Unit IV LP 1 (Lesson 8)

“When an unbalanced force acts on an object, the object will be accelerated. The

acceleration will vary directly with the applied force and will be in the same

direction as the applied force. It will vary inversely with the mass of the object.”

EVD 17

EVDPhysical Forces

Newton’s Second Law:

The Law of Momentum

Ref. Unit IV LP 1 (Lesson 8)

More momentum = more energy to change

1 lb @ 1 ft/sec = 1 unit of momentum Momentum & Intertia:

WORK AGAINST THE DRIVER

EVD 18

EVDPhysical Forces

The Law of Conservation of Momentum

Ref. Unit IV LP 1 (Lesson 8)

“For a collision occurring between two objects, the total momentum before the collision is equal to the

total momentum after the collision.”

“When two objects interact, exactly equal and opposite forces result; positive and negative forces

balance out.”

EVD 19

EVDPhysical Forces

The Law of Conservation of Momentum

Ref. Unit IV LP 1 (Lesson 8)

EVD 20

EVDPhysical Forces

Reaction “For every action there is an equal and

opposite ‘reaction.’”

Ref. Unit IV LP 1 (Lesson 8)

EVD 21

EVDPhysical Forces

Newton’s Third Law:

The Law of Reaction

Ref. Unit IV LP 1 (Lesson 8)

“For every action there is an equal and opposite reaction.”

EVD 22

EVDPhysical Forces

Newton’s Third Law:

The Law of Reaction

Ref. Unit IV LP 1 (Lesson 8)

Tires push “backward” on the road Road pushes “forward” on vehicle

EVD 23

EVDPhysical Forces

Centrifugal Force An inertial force which moves a body

away from the center of rotation.

Ref. Unit IV LP 1 (Lesson 8)

EVD 24

EVDPhysical Forces

Centripetal Force Forces directing the body towards the

center of rotation. Gravity Friction

Ref. Unit IV LP 1 (Lesson 8)

EVD 25

EVDPhysical Forces

Centripetal Force vs. Centrifugal Force Forces acting in direct contrast to

Centrifugal force.

Ref. Unit IV LP 1 (Lesson 8)

EVD 26

EVDPhysical Forces

Directional Control Steering Turning “Tracking” curves

Ref. Unit IV LP 1 (Lesson 8)

EVD 27

EVDPhysical Forces

Potential Energy Capability – i.e. Coiled Spring Relative to position “Stored” energy

Ref. Unit IV LP 1 (Lesson 8)

EVD 28

EVDPhysical Forces

Kinetic Energy Relative to motion = ½mv2

m = mass v = velocity

Ref. Unit IV LP 1 (Lesson 8)

EVD 29

EVDPhysical Forces

Control ONLY

VELOCITY & DIRECTION

Ref. Unit IV LP 1 (Lesson 8)

EVD 30

EVDPhysical Forces

Control Velocity

Acceleration Change in Velocity + Acceleration = increase - Acceleration = decrease

(Deceleration) Double Mass = Double Acceleration Generally thought of in the +

Ref. Unit IV LP 1 (Lesson 8)

EVD

Vehicle Characteristics

EVD 32

EVDVehicle Characteristics

Weight GAWR

Gross Axle Weight Rating GVWR

Gross Vehicle Weight Rating

Ref. Unit IV LP 2 (Lesson 9)

EVD 33

EVDVehicle Characteristics

Weight GVW Distribution

Ref. Unit IV LP 2 (Lesson 9)

+/- 7%

2/3

1/3

EVD 34

EVDVehicle Characteristics

Weight Center of Gravity

Ref. Unit IV LP 2 (Lesson 9)

EVD 35

EVDVehicle Characteristics

Suspension Axles

Rated to carry GVW Springs

Rated to carry GVW Wheels

Load rated hub Tires

Rated to carry GVW

Ref. Unit IV LP 2 (Lesson 9)

EVD 36

EVDVehicle Characteristics

Suspension Tires

40 sq. in. Road Contact 4/32 Min. Tread

Ref. Unit IV LP 2 (Lesson 9)

EVD 37

EVDVehicle Characteristics

Brakes ABS

Wet/icy roads Works with disc and drum

Auxiliary NFPA 1901 – 36,000 lbs. Engine (“Jake”) > 20 mph Automatic Transmission Retarders Driveline Retarders

Ref. Unit IV LP 2 (Lesson 9)

EVD 38

EVDVehicle Characteristics

Water/Liquid Surge NFPA 1901 NFPA 1902 Baffling

Ref. Unit IV LP 2 (Lesson 9)